Bilateral subthalamic deep brain stimulation in parkinson disease patients with severe tremor

Background: Previous studies have shown that subthalamic nucleus (STN) deep brain stimulation (DBS) improves tremor in Parkinson disease (PD). However, the patients included in those studies were unselected for tremor severity. Objective: We specifically assessed the effect of STN DBS on tremor in selected PD patients with severe tremor. Methods: Seventy-two PD patients who had received bilateral STN DBS were included. The effects of STN DBS on the off-medication tremor, the on-medication tremor, and the off-medication action tremor in patients selected as the worst one-third in each category at baseline were evaluated after a mean duration of > 2 years. Results: In patients with severe off-medication tremor, off-medication tremor score improved from 12.28 ± 2.80 at baseline to 1.93 ± 2.85 at the last follow-up (P <.001). The off-medication tremor in the off-stimulation state at the last follow-up was less severe than the preoperative off-medication tremor. In patients with severe on-medication tremor, on-medication tremor score improved from 6.17 ± 2.45 to 1.35 ± 2.58 (P <.001). In patients with severe off-medication action tremor, off-medication action tremor score improved from 5.08 ± 1.35 to 1.24 ± 1.42 (P <.001). Conclusion: STN DBS is effective for severe off-and on-medication tremor and off-medication action tremor in PD. Our findings suggest that STN DBS reduces PD tremor through, at least in part, its effect on the tremor-generating mechanism independent of dopaminergic transmission and that long-term electrical stimulation of STN might induce a structural or neurochemical change leading to the improvement of tremor.